As the interface between the maternal and fetal blood supplies, the placenta transports nutrients and oxygen to, and metabolic waste products and carbon dioxide away from, the fetus; it also produces hormones necessary for establishment and maintenance of pregnancy. To carry out these diverse functions, the placenta is comprised of functional units, called chorionic villi, which consist of loops of fetal capillaries surrounded by stromal cells, followed by cytotrophoblast, with the whole encased in a syncytiotrophoblast monolayer. As the placenta matures, the number of stromal cells and cytotrophoblast decrease significantly, resulting, at term, in an exchange interface composed primarily of fetal capillaries adjacent to the syncytiotrophoblast monolayer. Abnormalities in placental function are associated with common and clinically significant complications of pregnancy, including preeclampsia and fetal growth restriction. Given marked differences in placental structure and function between humans and experimentally tractable animal models, and the complex microarchitecture of the feto-maternal interface, there is a pressing need for in vitro models that can be used to experimentally probe the function of the human placenta. Traditional systems, such as choriocarcinoma cell lines, primary cytotrophoblast, placental explant cultures, and ex vivo perfusion of placental tissue, have significant limitations related to use of malignant cells to model non-malignant cells, failure to recreate the complex 3D relationships among different cell types, and/or short experimental life-span. Recently, placenta-on-a-chip approaches have been applied, but existing implementations lack the ability to recapitulate the native microenvironment, anatomical structure, and long-term function needed for detailed mechanistic studies. We will address these challenges by engineering a novel human placenta-on-a-chip in a microfluidic platform, which will recapitulate human placental microstructure and function. By using a rapid 3D bioprinting method, we are able to better replicate the intricate microarchitecture of the native maternal-fetal placental interface at term and incorporate each of the key human placental cell types, including placental microvascular endothelial cells, and primary cytotrophoblast or human trophoblast stem cells. The work will be accomplished in two aims by: (1) building the 3D placenta-on-a-chip and confirming the spatial placement, viability, and identity of the component cell types, and (2) performing detailed evaluation of our platform as a biomimetic model of placental function, including assessment of barrier formation, and the effects of varying glucose concentration and oxygen tension on biomolecular transport, production of placental hormones, and intracellular and extracellular RNA expression. Where appropriate, these results will be compared to those obtained from placental explants cultured in the same conditions. This work will produce a validated novel 3D bioprinted placental model that can be used to reveal the mechanisms of placental function and dysfunction in normal and complicated pregnancies.